To date, the lack of a suitable small animal model has hindered our quest to understand the immuno- and neuropathogenesis of HTLV-1 in an in vivo system. This is due to the inefficient fusion of HTLV-1 envelope with murine cells. Recently, a chimeric HTLV-1 virus has been developed that utilizes the envelope gene of the Moloney-murine leukemia virus thereby allowing fusion of the chimeric virus with murine cells. Utilizing this chimeric virus we have recently demonstrated that depletion of DCs enhances susceptibility to cell-free infection of HTLV-1 in CD11c-DTR-transgenic mice (Rahman et al., J. Immunol, in press). These mice are uniquely designed to selectively deplete DCs in vivo. Murine cells, unlike simian and human cells, are generally refractive to diphtheria toxin (DT). The fusion of DTR transgene to the CD11c promoter (largely expressed in murine splenic DCs) in CD11c-DTR-Tg mice allows for the complete ablation of DCs in the presence of DT without affecting other APCs such as B cells and macrophages. This system has been used to study role of DCs in the pathogenesis of several viruses including LCMV, HSV-1, and recently HTLV-1 (Rahman et al., J. Immunol., in press). However, these mice still pose problem in studying human MHC class I-associated immune responses (such as those observed in HAM/TSP patients) due to the mouse MHC background. This issue has been addressed in a separate strain of mice, known as line HHD II, which express human HLA-A2.1 molecule and are knockout for the mouse H-2Db MHC class I molecule and beta2-microglobulin thereby carrying only human HLA class I molecules. We have previously demonstrated the immunization and induction of Tax 11-19-specific CTL response in these mice (Manuel et al., J. Leuk. Biol., 2009). The study proposed herein attempts to generate a new transgenic strain (HHD II/DTR-Tg) of mice to study HTLV-1 infection and subsequent HLA-A2-restrticted cellular immune response in the absence and presence of DCs. The newly generated strain could be further utilized to investigate mechanistic aspects of DC:T cell interaction during HTLV-1-mediated immunopathogenesis. The ability to selectively ablate DCs in vivo offers a powerful tool to explore the role of this unique cell population in various infection and disease models. The development of a new hybrid strain (HHD II/DTR-Tg), as proposed here, will greatly facilitate future studies of HTLV-1 immuno/neuropathogenesis in addition to providing a valuable tool to the scientific community in general. PUBLIC HEALTH RELEVANCE: The proposed studies are relevant to public health and will reveal significant information concerning the dendritic cells-regulated T cell responses during complex autoimmune/neuroinflammatory diseases such as HAM/TSP and multiple sclerosis. Additionally the results of these studies will shed light on the dynamics of immune cell interactions during chronic viral infections such as HTLV-1, HIV-1, hepatitis virus and herpes simplex virus.